The Optical Transport Network (OTN) is a technique of digital wrapper disclosed in 1999 to solve the problem of high capacity transmission for high speed Time Division Multiplexing (TDM) signals. The OTN defined in the version of 2003 can provide functions such as transmission, multiplexing, protection and monitoring management and so on for client layer signals, and the supported client layer signals are mainly Ethernet signals supported by the Synchronous Transmission Module Level N (STM-N) and Asynchronous Transfer Mode (ATM) and supported through the Generic Framing Procedure (GFP), and the defined rate levels are 2.5G, 10G and 40G. With the Internet Protocol (IP) normalization for the transport network bearing signals and the popularization of a 10G Local Area Network (LAN) interface, the bearing of 10 Gigabit Ethernet (10GE) on the OTN becomes an important problem. Therefore, the International Telecommunication Union Telecommunication Standardization Sector (ITU-T) developed the G.sup43 standard in 2007, which defined the way of the OTN transmitting 10GE signals.
A multiplexing system of a traditional OTN is extremely simple. And the rate levels are 2.5G, 10G and 40G, which correspond to an Optical channel Data Unit (ODU)1, ODU2, ODU3 respectively. Services of Constant Bit Rate (CBR) are mapped to corresponding ODUks in the way of Asynchronous Mapping Procedure (AMP) or Bit-synchronous Mapping Procedure (BMP), and Packet services are mapped to the ODUks in the way of GFP, and then these ODUks are mapped to corresponding Optical channel Transmission Unit (OTU)ks. Certainly, the ODUs with low rate level also can be multiplexed to the ODUs with high rate level as shown in FIG. 1.
In order to adapt for multiple services, a new concept of High Order (HO) ODU and Low Order (LO) ODU is introduced in the OTN, as shown in FIG. 2, counting from the left in FIG. 2, the first column is the LO ODU, the rate levels in all frames, such as the rate level of the ODU3, are marked as ODU3(L), and L is the Low Order; the second column is the HO ODU, the rate levels in all frames, such as the rate level of the ODU3, are marked as ODU3(H), and H is the High Order. The HO/LO is identical with the concept of high order/low order container in a Synchronous Digital Hierarchy (SDH), the LO ODU is equivalent to that a service layer is used to adapt services with different rates and formats, and the HO ODU is equivalent to that a tunnel layer is used to provide transmission capability with certain bandwidths, and this layering structure supports the separation between a service board card and a circuit board card, and thus more flexibility and economy can be brought to the network deployment.
Compared with the G.709 in 2003, the G.709 Amendment 3 and G.sup 43 have changed greatly, and new signal types are introduced, which include ODU0, ODU2e, ODU3e1, ODU3e2, flexible ODU (ODUflex) and ODU4. The new optical channel data unit ODU0 with a rate of 1.244 Gb/s is firstly introduced, the ODU0 can be cross-connected independently, and also can be mapped to the high order ODU (such as the ODU1, ODU2, ODU3 and ODU4). In order to adapt to the transmission for 100GE services, the ODU4 is introduced, and the rate is 104.355 Gb/s.
The ODU1 is mapped to the ODU2 and ODU3 and the ODU2 is mapped to the ODU3 for keeping a 2.5G tributary time slot mapping and multiplexing way of the original version G.709, and it is added that the ODU1 is mapped to 1.25G tributary time slots of the ODU2 and ODU3 and the ODU2 is mapped to a 1.25G tributary time slot of the ODU3; all the other new rates (the ODU0, ODU2e and ODUflex) are mapped to the ODU1, ODU2, ODU3 and ODU4 in the way of 1.25G tributary time slot mapping and multiplexing. According to the G.sup 43, the ODU2e can be mapped to a 2.5G tributary time slot of the ODU3e1, and the ODU2e also can be mapped to the 1.25G tributary time slot of the ODU3e1. Most of the low order ODUs have the same number of tributary time slots in the high order. However, the ODU2e is an exception, and the ODU2e needs to occupy 9 1.25G tributary time slots or 5 2.5G tributary time slots in the ODU3, but ODU2e needs to occupy 8 1.25G tributary time slots in the ODU4. FIG. 3 is a detailed mapping and multiplexing path structure of the G.709 standard and G.sup43 standard.
The idea of Flexible ODU was widely discussed at the ITU-T Q11/SG15 intermediate meeting in September, 2008 and the ITU-T SG15 plenary meeting in December, 2008 initially. The initial thought of Flexible ODU is to provide bit transparent transmission of the OTN for client signals with arbitrary bit rates. The ODUflex is currently expected to be used for supporting those new bit rates which can not be mapped to the ODU2, ODU3 or ODU4 effectively. The ODUflex is taken as one low order ODU; the number of tributary time slots which one ODUflex occupies is arbitrary integral multiples of tributary time slots of the high order ODUk. The ODUflex bandwidth can be adjusted dynamically.
Currently, the size of Packet ODUflex is recommended to be: n×1.24416 Gbit/s±20 ppm (1n80), and the size of CBR ODUflex is 239/238 times of the client signal rate. The newly defined ODUflex will not provide mapping for the client signals which have been mapped to the ODU0, ODU1, ODU2 and ODU3 any more. With regard to CBR client signals, it is the first choice to map the client signals to the ODUflex through the BMP, and the ODUflex rate is 239/238 times of the client signal rate (above the 2.5G client signal rate). With regard to Packet service client signals, it is currently discussed that the client signals are mapped to the ODUflex by using the GFP; ODUflex=n*1.24416G, wherein 1n80; and the ODUflex bit rate is integer multiples of the number of tributary time slots of the high order ODUk.
After the G.709 standard of version 2003 is released, OTN devices are deployed abundantly after development for several years, and the latest G.709 standard are also changed largely, and after the newly deployed OTN devices are loaded with control planes, one end-to-end label switching path may control a great many old devices and new devices simultaneously, and the old devices can only support a 2.5G tributary time slot unit, and the new devices can support both the 2.5G tributary time slot unit and 1.25G tributary time slot unit; when one end-to-end label switching path goes through the old devices and new devices, the related interconnections during the management of end-to-end services become a technical problem existing in the reality.
An OTN standard always supports single stage ODU multiplexing. A subsequent result in an OTN v1 is one tributary time slot directly mapped by an ODU1 to an ODU3, which is not required to be firstly mapped to an ODU2. A motivation of the system architecture is to reduce complexity. In a normal evolution process of the system architecture, the newly added OTN functions are expected to have higher rates, and thus the concept of single stage multiplexing will be propelled forward more easily. That is to say, if all the rates increase upward, it may be very easy to use the single stage multiplexing continuously in the OTN system architecture.
As shown in FIG. 4, the network is the OTN network which has been deployed by operators, and the implementation of all node devices in the OTN network is based on the G.709 standard version released in 2003, and each node in the network does not support the ODU0 and ODUflex and is based on the 2.5G tributary time slot. With the larger-scale application of data services, the operators need to introduce applications of the ODU0 and ODUflex into the existing network, but when the applications of the ODU0 and ODUflex are introduced into the existing network, a problem of interconnection between the networks supporting the 1.25G Time slot (TS) and the deployed networks supporting the 2.5G TS exists, and if no other technologies are introduced, the operators have to upgrade all nodes in the existing network to support the ODU0 and ODUflex, and this certainly will destroy the OTN networks which have been invested by the operators and increase the additional costs of the operators.
In addition, after new OTN nodes are introduced into the existing network, how to control the end-to-end services is also the problem required to be solved. One end-to-end ODUk service may go through a great many old devices and new devices simultaneously, the old devices can only support the 2.5G tributary time slot unit, and the new devices can support both the 2.5G tributary time slot unit and 1.25G tributary time slot unit; when one end-to-end ODUk goes through the old devices and new devices, the related interconnections during the management of end-to-end services become a technical problem existing in the reality. Meanwhile, the problem of introducing services of the ODU0 and ODUflex into the OTN network to perform interconnection with the deployed networks also exists.